I'm sorry that you've been affected by this tragic event OP, it's obviously very closed to your heart. The thing is, never mind what other people do. You can't control and bend them to your will. You seem preoccupied with what you perceive to be the 'done thing' to do. There is no 'done thing'. 100 years ago there were different threats, not terrorism and not the media influence that there is now. Tragedies happened then just the same but I think people were generally more stoic and keen to put things behind them than they are now.
I think ReanimatedSGB's posts are pretty harsh, they made me wince - but I don't think she's wrong. Media sensationalism has skewed the public sense of reasonable dismay and distorted it into a misplaced sense of proprietorial outrage and determination to own, control and immortalise tragic (and newsworthy) events for extended periods of time. I personally don't think that's healthy and it achieves nothing other than perhaps some personal glorification for the person who publicly expresses their grief when they are several steps removed from the actual tragedy.
I remember Manchester last year, the cold feeling of shock and sadness. All very real. My own method of dealing with those feelings would be to quietly make a donation and/or do something good for somebody who needed it and/or pray and/or talk about it with somebody in RL. Those might be my methods, that doesn't mean that others need to share the same ones.
What I'm trying to say is that you/we should give the same tolerance to others that is extended to us. You were validated for your minute's silence as it was management-approved. The fact is that this seemingly wasn't enough for you, that instead of shrugging your shoulders, you followed this up with a thread seeking more validation in the form of outrage from others. You've changed your posts a little throughout the thread but tweaking them to fit won't work because we're not the borg, we have individual views and see different things in responses.
We all remember - or we don't - it's not mandatory to share that with anybody else and you are not entitled to demand that people do so.